This invention is relates to the manufacture of internal combustion engine pistons, such as, but not limited to, internal combustion engine pistons used in automobiles engines, treaded or crawler-type machinery, aeronautical engines, and marine based motors.
A piston is typically a highly-stressed engine component. While a piston is in motion, the top or crown of the piston may be subjected to high temperatures. Any grooves formed in the piston, for example grooves for compression rings, may be subjected to high impact stresses. Additionally, if the piston comprises a wrist pin port, the port may be subjected to adverse cyclical loads. These piston features undergo varying operational stresses, loads, temperatures, and other operation characteristics (hereinafter xe2x80x9coperational characteristicsxe2x80x9d) and may lead to different piston areas needing different mechanical attributes and qualities (also known as xe2x80x9cpiston characteristicsxe2x80x9d) to endure these operational characteristics.
A piston""s mechanical attributes may be determined by its properties. Pistons, such as, but not limited to, engine internal combustion pistons, often comprise aluminum alloys. These aluminum alloys include, but are not limited to, silumins, which can possess a silicon content in a range from about 11% to about 35%. Additionally, if the piston comprises silumin alloy-based compounds, the piston may also comprise hardening agents, such as silicon carbides (SiC) and aluminum oxides (Al2O3) The silicon and intermetallic particles in the alloys, in combination with the above agents, may enhance a material""s heat resistance and wear properties. However, a material""s resistance to metal fatigue and plasticity may decrease with the enhancement of its heat resistance and wear properties.
If a piston""s base materials do not provide it with desired properties, piston areas that may undergo stress can be formed from a material that can be hardened. The hardening may be conducted by incorporating at least one of ferrous-based alloy and ceramic materials. For example, a piston portion may include an ironholder, which is generally recognized as heat resistant that can reduce a compression ring groove wear. This piston portion can be reinforced by plasma-arc welding and injecting alloying constituents, such as nickel, iron, and other such reinforcing constituents, into the piston. The heat resistant nature of these materials protects the piston.
Piston design and production may depend on the desired application of the piston. For example, pistons can be formed by casting, as set forth Yu, et al. xe2x80x9cAluminum Alloys in Tractor Buildingxe2x80x9d, Machine Building, 1971. This casting method provides a relatively efficient and low cost production method, which permits casting of pistons with reinforcements thereon. These reinforcements include, but not limited to, piston ring holders and brackets. However, these aluminum-cast pistons are generally used in low dynamic loads (pressures) applications because the aluminum-cast pistons can only be subjected to low mechanical stress levels.
Another known piston production process comprises hot-deformation forging from an aluminum alloy billet, as disclosed in Yu et al., xe2x80x9cIsothermal Forging of Pistons from an Alloyxe2x80x9d, Forging Production, 1979. This forging method may be more expensive than a casting method, however, forging silumin-alloy pistons can provide enhanced mechanical properties. Thus, these silumin-alloy pistons can be used in applications that undergo powerful loads. The forging method typically is conducted for small and relatively simple pistons because of silumin""s low plasticity under hot-deformation forging conditions. Therefore, reinforcements are added to overcome this plasticity deficiency, for example brackets can be added by being mounted on a piston. This reinforcement can complicate a piston""s design and increase its production costs. Further, the forging method may be limited by forging temperatures that do not provide a desired quantity and size of the silicon and other hardening particles in the silumin-alloy. Therefore, known forging processes may, prevent an silumin-alloy piston from achieving-desired plasticity and mechanical properties. Therefore, a need exists for a piston production method that can produce pistons with desired plasticity and mechanical properties. Further, a need exists for a piston production method that overcomes the above-noted deficiencies. Also, a need exists for a piston production method for producing silumin-alloy pistons.
A piston production method produces an internal combustion engine piston. The method comprises forging a billet from an initial billet comprising an aluminum alloy that comprises silicon, intermetallic particles, and injected hardening particles, the forging is conducted under at least one of super-plasticity and hot deformation conditions; and heat treating the forged billet. The forging comprises forging at a temperature in a range from about 0.8 Tmelt to about 0.98 Tmelt. The forging also comprises forging at a strain rate in a range from about 5xc3x9710xe2x88x922 Sxe2x88x921 to about 5xc3x9710xe2x88x925 sxe2x88x921. The piston being formed with a configuration that enables other parts to be connected to the piston. The initial billet comprises at least one of: coarse grain silicon, intermetallic particles, and injected hardening particles having at least one of a lamellar, comprehensive shape, and fine grain silicon, intermetallic particles, and injected hardening particles being globular in shape. The silicon, intermetallic and injected hardening particle volume content is in a range from about 25% to about 60%, and an average grain size of the silicon, intermetallic, and injected hardening particles is less than about 15 xcexcm2.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.